This invention relates to a diagnostic system for a motor vehicle.
Today's extensive motor vehicles are becoming increasingly complex in their design and thus make it more and more difficult for service personnel to locate defects of systems of the motor vehicle. This is particularly true of intermittent defects that do not result in a breakdown of a system or the motor vehicle but may interfere with its operation.
Although the installation of more and more electronic systems has reduced the frequency of breakdown extensively, the complicated systems do not permit as good an insight as simple mechanical systems of the cause of the breakdown. Also, the service personnel must have extensive electrotechnical or electronical knowledge.
In DE-OS No. 32 29 411, an electronic arrangement with self-monitoring was therefore suggested for a motor vehicle. An electronic control system for the control of the operation of motor vehicle devices, in this case, is equipped with a defect detecting device that can determine defects in sections of the system. It also comprises a storage area for the storage of defect data and addresses, a defect display means and a microcomputer having an input and display unit that is assigned to the control system.
However, this system is relatively costly and requires a special vehicle information system with a separate display and input unit. Also, if by means of this system several electronic control units are to be monitored, a separate bus system is required in each case from the vehicle information system to the respective control system. However, this results in high wiring expenditures. The system is therefore costly and expensive and requires a lot of space for the additional elements. It is therefore difficult to house in the narrow space of a dashboard of a motor vehicle.
In the U.S. journal Electronics, Nov, 20, 1980, on Pages 113 to 122, electronic control systems are described that are equipped with a self-monitoring function. However, these use a central light unit or a central display field by means of which defect reports can be emitted from the control systems via a flashing code. It is true that this simple type of defect display is space-saving but the number of types of defects that can be shown is limited by the number of different and clearly detectable flash patterns because many information units that in each case appear only for a short period of time are difficult to combine into a clear and correct overall information.
A combination instrument, described in this journal as having a defect display in code form via an electronic speed indicator, reduces the above-described problems but is used only for the monitoring or diagnostic display of defects in the combination instrument itself. Control systems of other motor vehicle devices, on the other hand, cannot be connected to this diagnostic system. They require the above-described additional flashing light unit.
It is therefore the objective of the invention, starting from this known state of the art, to provide a diagnostic system for motor vehicles, the test unit and display system of which is the component of a combination instrument of the motor vehicle, in which case the test unit is connected with control systems that are to be monitored via a simple bus system for the transmission of serial, digital information. The serial bus includes a unidirectional stimulating line connecting the test unit and the plurality of control systems for initializing serial communication with individual control systems and a communication line for transferring serial digital information between the individual control systems and the testing unit. The communication line may be bi-directional for communication with bi-directional control systems or unidirectional for bringing information from the individual control systems to the testing unit. The display, which is used for displaying operational information in a combination instrument, is also used with the testing unit for displaying the requested defect reports received from storage areas of memories of the individual control systems. A plug is provided on the testing unit to receive a diagnostic plug to change the combination instrument with the testing unit and display into a diagnostic mode. The plug may also be used to receive an external diagnostic system to be used with the combined instrument and display or having its own display. A function changing switch is connected to the testing unit for controlling the diagnostic sequence and the diagnostic mode. The switch may include four switches. The first switch is used to select the control unit to be diagnosed and may include a counter for sequentially addressing the individual control systems in response to multilple activations of the first switch. A second switch is provided for initializing and requesting defect reports from the selected control units. In response to the activation of the second switch, the display shows the unit address, its identification, its requested defect report and query whether its storage area should be erased. A third switch, in combination with logic, is provided for erasing the defined storage area after the query and upon actuation of third switching. A fourth switch may be provided which causes automatic sequencing of the diagnostic sequence in the diagnostic mode.
The diagnostic system may also include vehicle self-diagnostics for recognizing and reporting defects during the operation of the vehicle. The display may also include requested behavioral responses from the driver in response to the self-diagnostic test. When the diagnostic system is in the diagnostic mode, its display takes precedence over any self-diagnostics. An external unit may be plugged into the testing unit or directly to the serial bus system. The testing unit is permanently connected with the control systems and in the diagnostic mode takes over the master control function of all the control systems.
The main advantages of the invention are its unproblematic construction, the use of components that are already contained in the combination instrument and a clear display of detected defect reports. By the use of a simple serial bus system, the wiring expenditures are also reduced. The system is therefore simple, sturdy, cost-effective and can also be housed in a space-saving way.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.